1. Technical Field
An anti-reflective coating (ARC) polymer used in a photolithography process, a method for preparing the disclosed anti-reflective coating polymer, and an anti-reflective coating composition comprising the anti-reflective coating polymer are also disclosed. The disclosed anti-reflective coating polymer usable in immersion lithography for the fabrication of a sub-50 nm semiconductor device.
2. Description of the Related Art
Photolithography processes are processes for the transfer of a semiconductor circuit pattern from a photomask to a wafer. They are one of the most important steps in determining the size and integration density of circuits of semiconductor devices.
In recent years, as the integration density of semiconductor devices has increased, new techniques have been developed for the fine processing required to fabricate the more dense semiconductor devices. Thus, there is an increasing need for fine processing techniques for photolithography processes. As the circuit linewidths are reduced, the use of short-wavelength light sources for illumination, such as KrF, ArF, F2 and EUV excimer lasers, and high numerical aperture lenses is required. EUV, F2, ArF and KrF lasers are preferentially used as light sources for their short wavelengths.
A number of studies on the development of sub-50 nm devices have been undertaken. In response to these studies, recent attention has been directed toward the development of suitable processing equipment and materials associated with the use of F2 and EUV as exposure light sources. Some technical solutions for the use of F2 are satisfactory to some extent, but there are the following problems: 1) the efficient mass production of high-quality CaF2 within a short time is limited, 2) since soft pellicles are likely to be deformed upon exposure to light at 157 nm, the storage stability is decreased, and 3) hard pellicles incur considerable production cost, and are difficult to produce on a commercial scale due to their nature of light refraction.
On the other hand, since suitable light sources, exposure equipment and masks are required to use an EUV laser, it is not yet suitable for practical use. Accordingly, the formation of finer high-precision photoresist patterns by using a photoresist adapted to the use of an ArF excimer laser has now become a key technical task. Under these circumstances, immersion lithography has recently drawn attention.
Dry lithography is a currently used lithography process, and is an exposure system where air is present between the exposure lens and the wafer. In contrast to dry lithography, immersion lithography, which corresponds to the numerical aperture (NA) scaling technique, is an exposure system wherein water is filled between an exposure lens and a wafer. Since water (refractive index (n)=1.4) is used as a medium for a light source in the immersion lithography, the NA is 1.4 times larger than that in the dry lithography using air (refractive index (n)=1.0). Accordingly, immersion lithography is advantageous because of the high resolution.
A problem encountered with the fabrication of a sub-50 nm semiconductor device is that an alteration in the critical dimension (CD) of a photoresist pattern inevitably takes place. During the process for the formation of an ultrafine pattern by standing waves, reflective notching diffracted light and reflected light from an underlayer can cause variation in the thickness of the photoresist. To prevent the reflected light from the underlayer, a light-absorbing material, called an “anti-reflective coating” is used between the underlayer and the photoresist. A bottom anti-reflective coating is between the underlayer and the photoresist layer. With the recent increase in the fineness of overlying photoresist patterns, a top anti-reflective coating (TARC) has also been used to prevent the photoresist pattern from being disrupted by the reflected and diffracted light. As the remarkable miniaturization of semiconductor devices makes overlying photoresist patterns increasingly fine, the use of a bottom anti-reflective coating only cannot completely prevent the patterns from being disrupted by scattered reflection. Accordingly, a top anti-reflective coating is used to prevent the disruption of the patterns.
However, since conventional top anti-reflective coatings for use in dry lithography are water-soluble (in the case of using KrF or ArF laser), they cannot be used in immersion lithography because water is used as a medium for a light source in immersion lithography.
Accordingly, an ideal top anti-reflective coating for use in immersion lithography must satisfy the following requirements: (1) the top anti-reflective coating must be transparent to a light source; (2) the top anti-reflective coating must have a refractive index between 1.4 and 2.0, depending on the kind of an underlying photosensitive film (i.e. photoresist) to be used; (3) when the top anti-reflective coating composition is coated on an underlying photosensitive film, it must not dissolve the photosensitive film; (4) the top anti-reflective coating must not be soluble in water upon light exposure; and (5) the top anti-reflective coating must be soluble in a developing solution.
The above-mentioned requirements make the development of a suitable top anti-reflective coating for use in immersion lithography very difficult. Thus, a strong need exists for the development of a top anti-reflective coating for use in immersion lithography which is water-insoluble and can minimize the alteration of the critical dimension (CD).